Tri-Heart Plus Oral Heartworm Preventive by Merck
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Tri-Heart® Plus Chewables by Merck

RX - Tri-Heart Plus Chewable Tablets 68mcg ivermectin/57mg pyrantel (1-25 lb dogs)
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Frequently Asked Questions

Q.  Is there a brand name equivalent to Tri-Heart Plus?
A.  Yes. Heartgard Plus is an FDA-approved alternative to Tri-Heart Plus that contains the exact same active ingredients, Ivermectin and Pyrantel, in the exact same amounts as Tri-Heart Plus. Heartgard Plus is beef-flavored.

Q.  What is heartworm disease and why is it bad for my dog?
A.  Adult heartworms lay very tiny larvae called microfilariae, which circulate in the blood. They enter a mosquito when it sucks the blood of an infected animal. They mature in the mosquito and then enter the animal's skin when an infected mosquito bites the animal. When the larvae reach about 3 inches, they migrate to the animal's heart where they grow into adults, sometimes reaching a length of 14 inches.

Severely infected dogs can have up to several hundred heartworms in their hearts and vessels. The adult worms can obstruct the different chambers of the heart and the various large blood vessels leading to and from the heart and lungs. In severe infections, other organs, such as the liver, can also be damaged.

Q.  Does my dog need a test before I start giving him Tri-Heart Plus?
A.  The American Heartworm Society advises that all adult dogs being started on a heartworm preventative for the first time be tested. After that, periodic, but not necessarily annual re-testing should be performed. The frequency of testing should take into account variables such as:
  • Prevalence of heartworm disease in the area
  • Missed or late doses of heartworm preventative
  • The dog's lifestyle
In areas where the mosquito season in not year-round, puppies born after the mosquito season do not need to be tested. For instance, in Northern Wisconsin, puppies born in January do not need to be tested. Consult with your veterinarian to determine the appropriate testing schedule for your dog.

Q.  How often should I give this medication to my dog?.
A.  Tri-Heart Plus is meant to be given every 30 days. When you start your dog on Tri-Heart Plus, make sure to give it to him on the same day every month.

Q.  When should I start giving my dog Tri-Heart Plus during the year?
A.  Remember that Tri-Heart Plus kills larvae your dog was exposed to in the preceding 30 days, so if you give your dog a preventative seasonally, give it to him a month after the first mosquito appears.

Q.  What if I miss a dose?
A.  If the interval between doses exceeds 30 days, ivermectin's efficacy can be reduced. Therefore, if you miss a dose, give the Tri-Heart Plus as soon as you remember that you missed it. We also recommend that testing the dog for heartworm infection 6-1/2 months after the missed dose.

Q.  I have heard that Collies and other herding breeds have trouble with ivermectin. What can you tell me about this?
A.  Collies and related breeds are known to have sensitivity to ivermectin. The dose of ivermectin in a monthly heartworm preventative is relatively low.

Q.  When should I start giving my puppy Tri-Heart Plus?
A.  You can start giving Tri-Heart Plus after your puppy reaches 6 weeks of age.

Drs Foster and Smith Articles

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